The invention relates to a sonde designed, in particular, for taking a plurality of fluid samples in a single operation.
This sonde which is particularly adapted to taking samples of the fluids present down an oil well in production, is never the less not limited to that application. In particular, it may also be used for taking samples in the food industry and in the oceanographic industry.
Most existing sondes for taking fluid samples operate in accordance with the principles described in the U.S. Pat. No. 3,095,930.
In such prior sampling sondes, a liquid such as oil is initially inserted into a chamber provided for this purpose in the tubular body of the sonde, and it serves to keep a piston in a rest position. While the piston is in this position, no fluid is admitted into a sampling chamber which communicates with the outside via an orifice formed in the sonde body. A sample-taking operation is triggered by a remote control device which puts the chamber containing the liquid into communication with a chamber containing air at a pressure which is rather very low compared with the outside pressure, said air chamber being likewise provided in the sonde body. Depending on circumstances, the remote control device may be a pyrotechnical device, an electrically controlled valve, etc. A regulator, such as a choke, is placed between the chamber which initially contains the liquid and the chamber containing air so as to prevent the liquid from being transferred too quickly under the effect of the very high pressure normally to be found downhole.
The above description illustrates the complexity of existing sampling sondes, which gives rise in practice to relatively lengthy and tedious preparations and implementation. In particular, the chamber containing the liquid must be filled with care since any air inside this chamber would lead to an error in the volume of the sample taken and would consequently give rise to error in the analyses subsequently performed on that sample.
Proposals have also been made, in particular in the European patent application No. EP-A-0 148 696, to insert into a single well either a plurality of sampling sondes or else a sonde comprising a plurality of sampling devices so as to enable a plurality of samples to be taken during a single descent.
This is advantageous since it reduces the inactive time of the well when several samples need to be taken in succession. However, due to the complexity of the sampling devices the number of samples which can be taken in this way during a single descent is limited by the size of each sampling device.
Further, the procedure for making use of each sampling device remains lengthy and tedious and is now multiplied by the number of devices to be inserted into the well, and this may not be acceptable for a well which is in production.